When using drying tubing (for example, Nafion) for sampling, the CO2 concentration of the dry sample will be slightly higher than in the wet sample. This is due to water condensing off the warm, humid gas sample as it cools down. In a sampling environment with humidity and temperature higher than ambient air, the CO2 concentration is diluted by the volume that the water vapor occupies. If water vapor is removed from the sample, the fractions occupied by other gases, including CO2, will increase accordingly.
CO2 dilution coefficients for GMP80P sampling methods at 23 °C (±2 °C) ambient temperature lists the three sampling methods of GMP80P and gives the dilution coefficients for each type of method. When you have the CO2 measurement value shown by Indigo80, you can use the coefficients given in the table to calculate the actual gas concentration in the sampling environment:
Temperature of sampled gas (°C) | ||||||||||
Method | +20 | +25 | +30 | +35 | +37 | +40 | +45 | +50 | +55 | +60 |
Steel pipe | 1.000 | 1.000 | 0.995 | 0.988 | 0.984 | 0.976 | 0.962 | 0.944 | 0.922 | 0.897 |
Plastic tube | 1.000 | 0.998 | 0.991 | 0.982 | 0.977 | 0.968 | 0.952 | 0.932 | 0.908 | 0.881 |
Nafion + plastic tube | 0.991 | 0.984 | 0.976 | 0.965 | 0.960 | 0.953 | 0.939 | 0.923 | 0.905 | 0.885 |